The present invention relates to an electrochemical fuel cell assembly including a cell voltage monitor; and more particularly to an electrical connecting device which may be used to monitor cells within a stack.
Fuel cells have been used as a power source in many applications. Fuel cells have also been proposed for use in electrical vehicular power plants to replace internal combustion engines. In proton exchange membrane (PEM) type fuel cells, hydrogen is supplied to the anode of the fuel cell and oxygen is supplied as the oxidant to the cathode. PEM fuel cells include a xe2x80x9cmembrane electrode assemblyxe2x80x9d (MEA) comprising a thin, proton transmissive, non-electrically conductive, solid polymer membrane-electrolyte having the anode on one of its faces and the cathode on the opposite face. The MEA is sandwiched between a pair of electrically conductive elements which (1) serve as current collectors for the anode and cathode, and (2) contain appropriate channels and/or openings therein for distribution of the fuel cell""s gaseous reactants over the surfaces of the respective anode and cathode catalysts. A typical PEM fuel cell and its membrane electrode assembly (MEA) are described in U.S. Pat. Nos. 5,272,017 and 5,316,871, issued on Dec. 21, 1993 and May 31, 1994, respectively, and assigned to General Motors Corporation, assignee of the present invention, and having as inventors Swathirajan et al.
A plurality of individual cells are commonly bundled together to form a PEM fuel cell stack. The term fuel cell is typically used to refer to either a single cell or a plurality of cells (stack) depending on the context. A group of cells within the stack is referred to as a cluster. Typical arrangements of multiple cells in a stack are described in U.S. Pat. No. 5,763,113, assigned to General Motors Corporation.
In most fuel cell assemblies, current is drawn from the fuel cell stack via a pair of bus plates, one of which is positioned at each end of the fuel cell stack. The fuel cells are stacked between the bus plates, which are typically made of copper or coated copper. Very often individual cells of the stack are contacted for monitoring individual cell voltages or currents, and/or for control or charging/discharging purposes. In most cases, these electrical contacts are not intended to carry the entire stack current, but are capable of providing electrical connection to individual fuel cells or clusters within a stack.
In mass production, an electrical connecting device is needed which is easy to handle and to install, and which provides reliable electrical contact with certain components of a fuel cell stack. It may be desirable to provide, in a single device, groups of contacts that always communicate with the same type of fuel cell component within the stack, or which contact the fuel cell stack at regularly spaced intervals along the length of the stack.
One problem with monitoring individual fuel cells or clusters of cells within a stack is the difficulty of attaching an electrical connector to the electrically conductive elements. For example, for a fuel cell which is designed to generate significant power output, a large number of bipolar plates are provided which require a large number of connections. Perhaps more importantly these connectors are being attached to plates located in close proximity to each other and with distances between the plates that vary from one plate to the next. All of this makes it difficult to make electrical connections.
It is particularly difficult to make connections using a connector capable of encompassing a large number of plates. Although the plates have a substantially uniform spacing therebetween, this spacing between the plates can vary slightly within acceptable tolerances. These slight differences in the spacing from one plate to the next can result in meaningful differences between the theoretical location of a particular plate and the actual location of that plate due to tolerance stack-ups. Thus, individual prior art connectors have typically been limited to connection with a relatively small number of successive plates to minimize the effect of tolerance stack-ups; for example, 8 to 16. Consequently, a single electrical connector which is capable of connecting with the closely spaced plates along the entire length, or at least a significant part of the length, of a fuel cell by adjusting for tolerance stack-ups is desired.
In accordance with a first aspect of the present invention, a connector for electrically connecting to a series of closely spaced plates having a substantially uniform spacing therebetween is provided. A plurality of recesses are located along the length of an elongated elastomeric member. A plurality of electrical contacts is also included and each of the plurality of contacts is associated with the elastomeric member in registration with one of the plurality of recesses. The elongated elastomeric member is adapted to expand or compress along its length to receive one of the closely spaced plates in each of the plurality of recesses and to thereby register each of the plurality of electrical contacts with a corresponding contact point on one of the closely spaced plates.
In accordance with yet another aspect of the present invention, a connector for electrically connecting a series of closely spaced plates is provided which includes an elongated elastomeric strip adapted to adjust to any tolerance variation in the substantially uniform spacing between the plates. A segment of the elastomeric strip is confined under compression between two adjacent members. The two adjacent members are either two adjacent closely spaced plates or two adjacent members of a single plate.
In accordance with another aspect of the present invention, a method of providing electrical connection to a series of closely spaced plates is provided. The method includes associating a plurality of electrical contact points with an elongate elastomeric strip. A segment of the elongate elastomeric strip is compressed and the compressed segment is placing between a pair of adjacent members of the series of closely spaced plates. At least one of the plurality of contact points is located in contact with one of the closely spaced plates by allowing the compressed segment to push against the pair of adjacent members to generate a force which pushes at least one of the plurality of contact points against the one of the closely spaced plates.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.